I wonder if anyone can give me any tips on logical way to start setting up an XYchain? My current method is just bumbling around, starting with a bi-value cell with a candidate that appears fairly frequently in the puzzle and that I'd like to eliminate WHEREEVER my chain happens to end up.Case in point: here's my notes to myself on the BrainBasher1-4-08SuperHard puzzle:Swordfish on 6=>r4c9<>6XychainOn6 r8c7-r8c3-r7c1-r5c1-r4c1-r4c8-r9c8=>r9c7<>6, r9c9<>6XychainOn4 r9c9-r9c8-r8c7-r8c3-r6c3-r4c1-r4c6=>r6c6<>4XychainOn4 r6c3-r4c1-r4c6=>r6c6<>4XychainOn4 r9c7-r9c4-r7c4-r7c1-r4c1-r5c1-r5c3=>r5c7<>414 16 16 16 69 19 14 (saved clps)

I think the final XYchain would have broken the puzzle in the first place, (still too lazy to start puzzle over again to find out) precluding all that thrashing around.Any hope of aiming at the right place initially? Should I post the puzzle for you guys to analyze?

After removing the three 6s it still took a couple of xy wings to finish.

As for xy chain tips.. you're doing fine. When you find a chain, be sure not to miss any eliminations. Keep an eye out for continuous loops, like the one above.

I read, or attempted to read, the definition of nice statements and gave up on it. I can follow your loop 'nicely' but don't understand the cancellations. Anyway, what I wanted to know if there was if there was a better aiming point for my XYchains then shooting in the dark the way I'm doing now. Thanks all.

stumble wrote:Anyway, what I wanted to know if there was if there was a better aiming point for my XYchains then shooting in the dark the way I'm doing now. Thanks all.

Okay, here's a few suggestions for finding XY-Chains.

1) Choose a starting cell, e.g. [r2c2], and an ending cell, e.g. [r8c8], that have 2-3 candidates between them.

2) If all of the cells they mutually see fail to contain the common candidate, e.g. 6, then return to (1).

3) When possible, see if eliminating the common candidate is (obviously) beneficial before searching for a chain.

4) Now, you need to find a chain of (currently existing) bi-value cells that force the common candidate to be true in either the starting or ending cell. This chain will always start with the non-common candidate being assumed true; e.g. [r2c2]=4 or [r8c8]=8. I don't have any suggestions on how to shortcut finding a chain.

5) Once you find a chain, remember to eliminate the common candidate from all of the cells the starting cell and ending cell mutually see.

6) Some starting cells work with multiple ending cells. Don't assume that you're done with a starting cell once you find an XY-Chain for it.

7) One XY-Chain may eliminate a candidate in a cell with three candidates. This may allow a subsequent XY-Chain that didn't exist prior to the elimination. Go back and check!

8) Finally, there's no reason that a starting cell can't have a separate XY-Chain for each candidate. Don't stop after finding an XY-Chain based on one candidate in the starting cell.